During the past several decades, the emergence and wide adoption of digitally encoded video produced by a variety of electronic recording devices and computer systems for electronic transmission and electromechanical and electro-optical-mechanical storage has generated significant ongoing research efforts to develop ever more capable and efficient video-encoding methods. A variety of different video-coding standards have emerged, including various Motion Picture. Experts Group (“MPEG”) standards, and Video Coding Experts Group (“VCEG”) standards, including MPEG-2, MPEG-4, and H.264.
In addition to specifying a digital format for encoding sequences of digital images, or frames, that, together compose videos, digital video-encoding methods and systems seek to compress digital representations of videos for efficient storage and transmission while preserving, as much as possible, the appearance of the original videos in decompressed and displayed video sequences. In general, there are significant tradeoffs between the degree to which a video sequence can be compressed and the fidelity of decompressed and displayed video with respect to the original video. The greater the compression, in general, the less fidelity obtained from decompressed and displayed video sequences.
Video-sequence compression employs a variety of techniques, described in detail below. One technique involves representing small regions of frames, referred to as “macroblocks,” as motion vectors, rather than as intensity-and-color values for pixels in the regions. Motion vectors are references to similar macroblocks in preceding or following frames. Currently available techniques and standards constrain the number of macroblocks, and frames containing macroblocks, that can be referenced for encoding of a given macroblock within a particular frame. When, under these constraints, a suitable motion-vector encoding of a macroblock cannot be obtained, less efficient encoding schemes are employed. Researchers and developers of video-encoding methods and systems continue to seek flexible and efficient video-encoding techniques that provide for increased levels of compression.